Sprint supposed to have stopped extending contracts upon changing plans. If I'm not mistaken, a change of service and/or pricing which you deem to be considered "materially adverse to you" (should be in subscriber's agreement) should get you OUT of your contract with no ETF. However, if you want to stay with Sprint...that is what you can use to leverage retentions/cancellations/account services to keep your current plan as is...without having to be forced to upgrade.
a little video from
the Consumerist talks about this exact thing, but it was from sometime ago...so use this tactic at your own risk.